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Inside Macintosh: Memory /

Chapter 2 - Memory Manager / Memory Manager Reference

Memory Manager Routines / Setting the Properties of Relocatable Blocks

HLock

You can use the HLock procedure to lock a relocatable block so that it does not move in the heap. If you plan to dereference a handle and then allocate, move, or purge memory (or call a routine that does so), then you should lock the handle before using the dereferenced handle.

PROCEDURE HLock (h: Handle);

h

A handle to a relocatable block.

DESCRIPTION

The HLock procedure locks the relocatable block to which h is a handle, preventing it from being moved within its heap zone. If the block is already locked, HLock does nothing.

ASSEMBLY-LANGUAGE INFORMATION

The registers on entry and exit for HLock are

Registers on entry
A0	Handle to lock

Registers on exit
D0	Result code

RESULT CODES

noErr	0	No error
nilHandleErr	-109	NIL master pointer
memWZErr	-111	Attempt to operate on a free block

SEE ALSO

If you plan to lock a relocatable block for long periods of time, you can prevent fragmentation by ensuring that the block is as low as possible in the heap zone. To do this, see the description of the ReserveMem procedure on page 2-55.

If you plan to lock a relocatable block for short periods of time, you can prevent heap fragmentation by moving the block to the top of the heap zone before locking. For more information, see the description of the MoveHHi procedure on page 2-56.